U.S. patent number 5,602,554 [Application Number 08/512,425] was granted by the patent office on 1997-02-11 for active array antenna with multiphase power for active modules.
This patent grant is currently assigned to Martin Marietta Corp.. Invention is credited to Bruce M. Cepas, John G. Ferrante, Eric L. Holzman, Wilbur Lew.
United States Patent |
5,602,554 |
Cepas , et al. |
February 11, 1997 |
Active array antenna with multiphase power for active modules
Abstract
A radar system which uses an active phased-array antenna
achieves improved clutter improvement factor (CIF) by powering the
various transmit-receive (TR) modules of the antenna with direct
voltage (DC) derived from a plurality of phases of the power-line
alternating current (AC). Each TR module receives power which
originates with one phase of the source AC. The phases are selected
so that the modulation of the radio-frequency (RF) signals by each
TR module tends to cancel in the summed signal from the array
antenna.
Inventors: |
Cepas; Bruce M. (Mt. Laurel,
NJ), Lew; Wilbur (Mt. Laurel, NJ), Holzman; Eric L.
(Medford, NJ), Ferrante; John G. (Wilmington, DE) |
Assignee: |
Martin Marietta Corp.
(Moorestown, NJ)
|
Family
ID: |
24039024 |
Appl.
No.: |
08/512,425 |
Filed: |
August 8, 1995 |
Current U.S.
Class: |
342/368 |
Current CPC
Class: |
H01Q
1/248 (20130101); H01Q 3/22 (20130101); H01Q
21/0025 (20130101) |
Current International
Class: |
H01Q
21/00 (20060101); H01Q 3/22 (20060101); H01Q
1/24 (20060101); H01Q 003/22 () |
Field of
Search: |
;342/368,371,372,376 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"Transformer for AC/DC Power Supply Using 15 Phase Full Bridge", by
Guenther et al, published at pp. 357-363 of Proceedings of the
Electrical Manufacturing Coil Windings Show, Cincinnati, OH, 1992,
of the International Coil Windings Association..
|
Primary Examiner: Issing; Gregory C.
Attorney, Agent or Firm: Meise; W. H. Nieves; C. A. Young;
S. A.
Claims
What is claimed is:
1. An array antenna adapted to be energized from a source of
alternating current, said antenna comprising;
a plurality of antenna elements;
a plurality of active modules coupled to said antenna elements for
the flow of RF signals therebetween, each of said active modules
comprising active means for operating on said RF signals, said
active modules being grouped into a plurality of energization sets
so that each module is associated with only one of said
energization sets;
a source of multiphase AC line power;
AC-to-DC conversion means coupled to said source of multiphase AC
line power and to said active modules, for separately converting
each phase of said multiphase AC line power into DC, to thereby
form a plurality of DC sources, each derived from a different one
of said phases, and for coupling each of said plurality of DC
sources to a different one of said energization sets for
energization thereof.
2. An antenna according to claim 1, wherein said AC-to-DC
conversion means comprises a plurality of AC-to-DC conversion means
coupled to said source of multiphase AC line power, for generating
a plurality of intermediate direct voltages, each derived from a
different one of said phases of said AC line power, and further
comprising DC-to-DC conversion means coupled to each of said
AC-to-DC conversion means and to said active modules, for
converting said intermediate direct voltages into voltages suitable
for powering said active modules.
3. An antenna according to claim 1, wherein said a source of
multiphase AC line power further comprises:
multiphase AC transformation means, adapted to be coupled to a
source of AC line power having a first number of phases, for
converting said AC line power having a first number of phases into
said multiphase AC, where said first number of phases is less than
the number of phases in said multiphase AC.
4. An antenna according to claim 3, wherein said first number of
phases is one, and said number of phases in said multiphase AC is
four.
Description
FIELD OF THE INVENTION
This invention relates to active array antennas, and more
particularly to such array antennas in which the transmit-receive,
or transmit- or receive-only modules are grouped into sets, and
each set receives direct energizing voltage derived from a
different one of a plurality of phases of the alternating-current
source.
BACKGROUND OF THE INVENTION
Active array antennas for use in radar systems may include many
hundreds or thousands of antenna elements to achieve the desired
beamwidth and number of beams. Each of the antenna elements, or
each set of the antenna elements of an active array, is associated
with an active module. Each active module operates on the
radio-frequency (RF) signal transduced by the associated
element(s), as by amplification, phase shifting, amplitude control,
or the like. In this context, "active" means a module which
requires, for its operation, electrical bias separate from the RF
signals on which it operates. Passive RF operations are possible,
such as phase shift, but in the absence of active elements, they
can only be changed by mechanical means, as by adjusting a
capacitor. Since one of the major advantages of an array antenna is
that it may be "agile" (the beam can be quickly slewed and changed)
when electronically controlled, almost all array antennas include
active modules associated with the antenna elements. Such modules
may be transmit-only, receive-only, or they may be transmit-receive
(T/R or TR) modules when the array antenna is used for both
transmission and reception. U.S. Pat. No. 5,339,086, issued Aug. 6,
1994, in the name of DeLuca et al., describes in general how TR
modules are controlled in an array antenna context. U.S. Pat. No.
5,280,297, issued Jan. 18, 1994 in the name of Profera, describes
the use of active modules for retransmission in the context of a
reflectarray.
In a radar context, the transmissions, as for example transmit
pulses, must have relatively high power. The power is achieved by
"summing in space" the powers radiated by each of the antenna
elements. Since the radiated RF power originates within the TR
modules, the total energization power applied to the TR modules
must be at least the sum of the transmitted RF power plus the
losses in the TR module. In turn, the power requirements of a
powerful radar system may be considerable, with the principal
portion of the power going to the TR modules. Thus, operation of a
radar system using an active array antenna requires a power source
for the TR modules. U.S. Pat. No. 5,173,706, issued Dec. 22, 1992
in the name of Urkowitz, describes an active array antenna in the
context of a radar system.
Ideally, the active portions of at least the analog components of a
radar system are energized by pure direct voltage, also known as
direct current (DC), to avoid the effects of noise on the direct
voltage buses. For generating low-noise direct energizing voltages
for the radar system, elaborate power-line filters and regulators
are the norm. Those skilled in the art know that, notwithstanding
these precautions, the direct energizing voltage always contains
some residual noise, and that the circuits which are driven thereby
should ideally be designed to reject energization voltage noise.
Even when so designed, some residual modulation of the RF by the
noise can occur, generally at the power-line frequency of 60 Hertz
(Hz.) or its harmonics for ground-based systems, and 400 Hz. or its
harmonics for airborne systems. The residual modulation, in turn,
tends to adversely affect some of the normal functions of the
radar, and especially those which depend for their operation upon
cancellation of like signals, in which minuscule differences
between the signals being canceled may result in an undesired
residual signal. One function which is adversely affected by
energization voltage noise is the clutter improvement factor (CIF),
in which repetitive signals (clutter) are phase-shifted in
alternate time periods, and added together in such a manner that
they cancel.
Improved array antenna systems are desired.
SUMMARY OF THE INVENTION
An array antenna, which is adapted to be energized from a source of
alternating current, includes a plurality of antenna elements. A
plurality of active modules is coupled to the antenna elements in
such a manner as to allow for the flow of RF signals therebetween.
Each of the active modules comprises active devices for operating
on the RF signals passing through the module. The active modules
are grouped into a plurality of energization sets, so that each
module is associated with one of the energization sets. An AC-to-DC
converter is coupled to a source of multiphase AC line power and to
the active modules, for separately converting each phase of the
multiphase AC line power into DC. Thus, there are a plurality of DC
sources, each of which is derived from a different one of the
phases of the multiphase AC line power. Each of the plurality of DC
sources is coupled to a different one of the energization sets, for
energization of the active modules thereof. In a particular
embodiment of the invention, the AC-to-DC converter includes a
plurality of AC-to-DC converters coupled to the source of
multiphase AC line power, for generating a plurality of
intermediate direct voltages, each derived from a different one of
the phases of the AC line power, and further includes a DC-to-DC
converter coupled to each of the AC-to-DC converters and to the
active modules, for converting the intermediate direct voltages
into voltages suitable for powering the active modules. A
particular antenna may be powered by a multiphase AC transformer,
adapted to be coupled to a source of AC line power having a first
number of phases, for converting the AC line power having a first
number of phases into the multiphase AC, where the first number of
phases is less than the number of phases in the multiphase AC.
DESCRIPTION OF THE DRAWING
FIG. 1 is a simplified diagram, partially in block form and
partially in schematic form, illustrating an energizing power
system according to the invention for a plurality of TR
modules;
FIG. 2 is a simplified block diagram, illustrating another possible
arrangement for powering TR modules according to the invention;
FIG. 3 is a simplified block diagram, illustrating yet another
possible arrangement for powering TR modules according to the
invention; and
FIG. 4 is a plot of noise suppression as a function of phase error
for a four-phase system.
DESCRIPTION OF THE INVENTION
In FIG. 1, a source of single-phase 60 Hz. alternating current (AC)
line voltage is illustrated by a generator symbol 10. A four-phase
transformer 12 has its primary winding 14 connected to AC source
10, and produces one of four phases at each of its four secondary
windings 0, 90, 180, and 270. More particularly, winding 0 produces
reference phase zero, winding 90 produces AC at a phase of
90.degree. at 60 Hz. relative to reference phase 0, winding 180
produces AC at a relative phase of 180.degree., and winding 270
produces AC at a relative phase of 270.degree.. At the right of
FIG. 1, a plurality of TR modules are illustrated as blocks 120t,
122t, 124t, and 126t. An AC-to-DC converter 20 is illustrated as
including two blocks, and converts the AC to direct voltage for
energizing the TR module or modules represented by block 120t.
Similarly, AC-to-DC converters 22, 24, and 26 are coupled to
windings 90, 180, and 270, respectively, for converting the AC of
their respective windings into DC for energizing the TR modules
represented by blocks 122t, 124t, and 126t, respectively.
An active array antenna may have thousands of antenna elements, and
a TR module for each element. Those skilled in the art know that
the solid-state devices which are appropriate for a TR module
require significant current at relatively low voltage. If the
conversion between AC and the DC energization voltage is performed
in one step, the power for all the TR modules must be distributed
at the same low voltage which is appropriate for direct
energization of a TR module. The voltage is likely to be less than
15 volts, and each module may require 100 milliamperes or more. For
an array with thousands of TR modules, the power buses would have
to be capable of carrying 100 amperes at 15 volts, which might
require buses of inconvenient size and weight. This problem is
ameliorated by two-step distribution, in which each. AC-to-DC
converter is made up of a first converter for converting AC to DC
at a relatively high voltage. The power is distributed at the
relatively high DC voltage, as a result of which the required power
can be distributed at a correspondingly lower current, and at a
location near the TR module(s) to be energized, is converted to a
lower DC voltage appropriate to powering the TR modules. The
conversion to a lower DC voltage is performed by a DC-to-DC
converter, which includes as a constituent thereof one or more
transformers, which result in converting the relatively high DC
voltage at low current into a relatively low voltage at a higher
current. Thus, in FIG. 1, AC-to-DC converter 20 includes an
AC-to-high-DC converter 20a and a high-DC-to-low-DC converter 20b,
which drives the TR modules associated with block 120t. Similarly,
AC-to-DC converter 22 includes an AC-to-high-DC converter 22a and a
high-DC-to-low-DC converter 22b, which drives the TR modules
associated with block 122t, AC-to-DC converter 24 includes an
AC-to-high-DC converter 24a and a high-DC-to-low-DC converter 24b,
which drives the TR modules associated with block 124t, and
AC-to-DC converter 26 includes an AC-to-high-DC converter 26a and a
high-DC-to-low-DC converter 26b, which drives the TR modules
associated with block 126t. The conductor buses extending between
each AC-to-DC converter and the following DC-to-DC converter may be
relatively long, since the power must start from a central
location, and arrive at the location of the TR modules which are to
be powered before the conversion to a lower DC voltage can be
made.
FIG. 2 illustrates another embodiment of the invention, in which
each AC-to-DC converter 20, 22, 24, 26 includes a single AC-to-DC
converter, which drives plural TR modules. In FIG. 2, AC power
arrives at AC-to-DC converter 20 from winding 0 of FIG. 1, and is
converted into relatively low DC voltage on a bus conductor 30b.
The low-voltage DC derived from phase 0 is distributed over bus
30b, in parallel or in common to a plurality of TR modules 120t1,
120t2, . . . 120tn. Similarly, the low-voltage DC derived from
phase 90 is distributed over a bus 32b, in parallel, to a plurality
of TR modules 122t1, 122t2, . . . 122tn, the low-voltage DC derived
from phase 180 is distributed over a bus 32b, in parallel, to a
plurality of TR modules 124t1, 124t2, . . . 124tn, and the
low-voltage DC derived from phase 270 is distributed over a bus
36b, in parallel, to a plurality of TR modules 126t1, 126t2, . . .
126tn. While the TR modules which receive energizing power
originating from any particular phase of energizing power are
illustrated as being side-by-side in FIG. 2, these TR modules are
each co-located or collocated with their respective elemental
antennas, and may be distributed throughout the area of the array
antenna, with TR modules powered from other phases interposed
therebetween.
The invention, as so far described, has the advantage that the
residual power-line noise, including harmonics of the power-line
frequency (60 or 400 Hz.) at frequencies potentially ranging up to
several thousand Hz, which is coupled to the TR modules appears at
different phases in different TR modules, and thus tends to cancel
in the sum RF signal at the output of the beamformer. It should be
emphasized that, while the TR modules of each set 120t, 122t, 124t,
and 126t are desirably "near" each other insofar as the length of
DC distribution bus 30, 32, 34, and 36, respectively, they may not
be, and in general probably are not "near" each other in terms of
mutual proximity of their respective radiating antenna elements in
the radiating aperture.
FIG. 3 illustrates another embodiment of the invention, in which
each AC-to-DC converter 20, . . . , 20n includes a plurality of
DC-to-DC converters, each of which drives plural TR modules. In
FIG. 3, AC power arrives at AC-to-DC converter 20a from winding 1
of FIG. 1, and is converted into relatively high DC voltage on a
bus conductor 130a. The high-voltage DC derived from phase 0 is
distributed over bus 130a to a plurality of DC-to-DC converters
20b1-20bn. Each DC-to-DC converter 20b1-20bn supplies DC, by way of
paths 130b1, . . . , 130bn to the associated TR modules 220t1, . .
. , 220tn; . . . ; 222t1, . . . , 222tn. Similarly, AC-to-DC
converter 20n receives phase n AC and converts it to DC in an
AC-to-DC converter 50a. The relatively high DC voltage from
converter 50a is applied to a plurality of DC-to-DC converters
50b1, . . . , 50bn, each of which converts the high voltage DC to
lower-voltage DC. The low-voltage DC produced by each DC-to-DC
converter 50b1-50bn is supplied to the associated TR modules 224t1,
. . . , 220tn; . . . ; 226t1, . . . , 226tn.
Multiphase transformers suitable for use as transformer 12 of FIG.
1 are known, and are available from, for example, NWL Transformers,
Inc. Rising Sun Road, Bordentown, New Jersey 08505. It is believed
that such transformers have "ring" windings comparable to
conventional "WYE" windings, and the various phases are derived
from combinations of various taps along the ring winding.
The output of the phased-array antenna may be considered to be the
common RF port in a receiving condition, or the RF signal which is
summed in space in a transmitting mode. The transmitted signal can
be sampled by use of a probe antenna which samples the transmitted
field. The noise power at the output of the antenna includes
components which arise from interaction, in the TR modules, of RF
signal with noise on the DC power buses. The noise contributions
attributable to the switching frequencies of the DC-to-DC
converters can be readily reduced by relatively simple filtration,
because of the high operating frequencies of the converters.
However, harmonics of the power-line frequencies are more difficult
to filter, and may appear on the buses. The noise power at the
output of the antenna, then is described by the equation ##EQU1##
where A is the total number of elemental antennas or radiators;
N is the number of transformer taps or different bus phases;
and
.phi..sub.i =i*.theta. is the relative phase of the i.sup.th tap,
and
.theta. equals 360.degree. /N.
Relative to the desired signal at the output of the antenna, the 60
Hz. harmonic noise is suppressed by S dB, where ##EQU2##
A realistic way to specify a transformer's output phase offset is
to specify a phase error range on each of the N taps. Thus, we
write .phi..sub.i as i*.theta..+-..delta..sub.i, where
.delta..sub.i is the phase error on the i.sup.th tap. If we solve
equation (2) for a large number of cycles of the transformer, each
cycle choosing the .delta..sub.i 's randomly within a specified
error range, we can determine the probability that a certain
suppression will be achieved for that range. FIG. 4 plots the noise
suppression for the four-phase transformer (ideal tap phase offset
equal to 90 degrees) versus tap phase error range. The plot locus
corresponds to a 100% probability of achieving the associated noise
suppression. Thus, from the plot, a phase error of .+-.4 degrees on
each transformer tap should result in a noise suppression of about
26dB at the output of the T/R modules.
Other embodiments of the invention will be apparent to those
skilled in the art. For example, while conversion from single-phase
AC to four-phase AC has been explicitly described, the conversion
could be to any number of phases.
* * * * *